Description:

Hematopoietic stem cells (HSC) reside in a complex microenvironment that regulates their function. The exact configuration of cells and intercellular contacts in the niche are poorly understood. We applied correlative light and electron microscopy (CLEM) to match fluorescent HSC tracked by light sheet microscopy in the same zebrafish embryo that was fixed and stained for EM. Micro-CT was used to orient and trim the embedded sample to isolate the niche. Serial block-face scanning EM was used to capture high resolution serial sections. Blood vessels observed in light and EM 3D data sets provided the anatomical markers needed to match the position of cells found using both techniques. We could confirm the position of a single round HSC with a large nucleus, little cytoplasm, and a ruffled membrane, that was lodged just under the vessel wall. This unique system for analysis of the ultrastructure of an endogenous HSC in an unperturbed niche will allow further functional and mechanistic studies at the subcellular level. Our goal is to gain novel insights into intercellular interactions between HSC and the surrounding supportive cells in the perivascular niche.